This application describes a highly integrated series of projects aiming to develop orexin-1 (OX1) receptor antagonists for treatment of tobacco dependence. Project 1 will utilize iterative medicinal chemistry based on structure-activity relationships (SAR) to discover new classes of potent and selective OX1 receptor antagonists. SAR will be used to optimize new classes of OX1 receptor antagonists for drug metabolism and pharmacokinetics (DMPK), and brain penetration properties. We have already generated excellent OX1 receptor antagonists as starting points for SAR based on our ongoing medicinal chemistry efforts. Project 2 will support SAR by testing new compounds in in vitro cell-based functional assays for OX1 receptors (and appropriate counter-screens) to determine potency and selectivity. We have already established and validated a range of OX1 receptor cell-based assays, and have successfully used these assays to identify starting points for SAR. Project 3 will test new classes of potent and selective OX1 receptor antagonists to identify those with the most favorable physiochemical and brain penetration profiles, and identify those least likely to have toxicity in humans. Project 4 will test the in vivo efficacy of novel OX1 receptor antagonists in cutting-edge behavioral procedures that assess addiction-related behavioral effects of nicotine. Importantly, have developed a new IV nicotine self-administration procedure for mice, and will assess novel OX1 receptor antagonists in wild type and OX1 receptor knockout mice to determine their behavioral selectivity. This integrated multidisciplinary research plan will capitalize on the unique drug discovery capabilities at Scripps Florida, and promises to yield novel therapeutic entities for the prevention of relapse in human tobacco smokers.